Specimens for virus isolation will be collected in the community of Tecumseh to identify the appearance of influenza virus in this well-defined population. To study past history of seeding or the occurrence of influenza viruses other than the prevalent strain in the community, the collected sera will be tested against antigens of various type A influenza viruses. To determine current and future patterns of infection, approximately 1000 individuals resident in Tecumseh will be recruited for prospective study. The aim here will be to follow a significant number of individuals of all ages to determine the effect of vaccination, the fall off in antibody level induced over time, the seeding of influenza viruses into the community, and the distribution of infection according to antibody status.